Before Pressing Cycle Start
Always verify the following before running any program:
Are you running the right program?...
If you can't confidently answer "yes," go back and check. Accidentally running the wrong program with the wrong setup could cause a serious crash.
Did you install the right tool?...
Many tools are alike. Always double check that tool number matches what the program asks for.
Is your workpiece secure?...
If it can wiggle it free, don't machine it.
Did you close the machine doors?...
This is what stands between you and a hungry spindle that flings sharp chips (and in the event of a crash, parts) in your direction.
Are you ready to press the Emergency Stop button?...
Also, did you read The Emergency Stop Button? If you haven't, go do that first.